Circuit breakers for electric power have a role to interrupt a fault current flowing in a transmission line when a fault occurs in a system, such as a ground fault or a short circuit fault. Such circuit breakers open when receiving interruption control signals generally from protective relays that have detected fault currents. Because such a protective relay outputs an interruption control signal immediately after the detection of a fault current, the time at which an interruption control signal outputs from the protective relay is at random with respect to the phase of voltage or current. Thus, the arc duration, which is from when the circuit breaker opens (when its electrode contact is separated) until when the fault current is interrupted at the next current zero point where it is possible to interrupt the current, can be short or long. When the arc duration is long, the amount of erosion of the electrode contact increases and the system restoration is delayed.
A conventional power switching control apparatus measures a current and, by using the time interval between the current zero points and the current gradient, estimates a time interval between future current zero points so as to control the opening timing such that the current is interrupted with the minimum arc duration (for example, Patent Literature 1).